Steam has been used in many different methods for the recovery of oil from subterranean, viscous oil-containing formations. There are many subterranean petroleum-containing formations in various parts of the world from which petroleum cannot be recovered by conventional means because the petroleum is too viscous to flow or to be pumped. The most extreme examples of viscous petroleum-containing formations are the so-called tar sand or bitumenous sand deposits. The largest and most famous such formation is the Athabasca Tar Sand Deposit in the northeastern part of the province of Alberta, Canada, which contains over 700,000,000 barrels of petroleum. Other extensive deposits are known to exist in the western United States and Venezuela, and smaller deposits exist in Europe and Asia.
The two most basic processes used for recovering viscous oil from a formation includes a "steam drive" process and a "huff and puff" steam process. Steam drive involves injecting steam through an injection well into a formation. Upon entering the formation, the heat transferred to the formation by the steam lowers the viscosity of the formation oil, thereby improving its mobility. In addition, the continued injection of steam provides a drive to displace oil toward a production well from which it is produced. Huff and puff involves injecting steam into a formation through a well, stopping the injection of steam, permitting the formation to soak and then producing oil through the original well.
Steam flooding operations for recovering heavy oil utilizing propane- or diesel-fired downhole steam generators are described in "Steam Generators Work Long Periods Downhole", Oil and Gas Journal, July 5, 1982, pp. 76 and 78, and "West Coast EOR Project Results Discouraging", Oil and Gas Journal, Aug. 9, 1982, pp. 82.
During steam flooding of a viscous oil containing formation or a formation-containing solid bitumen, occasionally steam flooding is interrupted. Viscous oil or solid bitumen becomes mobile at the elevated temperatures existing in a steamflood. When steam injection is interrupted, heavy oil containing bitumen or bitumen may enter the casing through the perforations, flow upwardly, cool, and solidify. This results in reduced or steam injectivity cessation which causes costly workovers and occasionally leads to complete well failures.
Therefore, what is needed is a method to prevent oil containing bitumen or bitumen from backflowing into the well and solidifying when steam injection is interrupted so as to prevent costly workovers and avoid complete well failures.